Field of the Invention and Related Art Statement
The present invention generally relates to an electric detonator of delay type, and more particularly, to an electric detonator which is preferably used in a multi-step explosion in which a number of explosives are ignited at different timings.
A known electric detonator of delay type comprises a pair of leg wires connectable to bus wires which are connected to an electric blaster, a capacitor for storing electric energy, an electric delay circuit including an electronic delay element and an electronic switching element, and an electric igniting portion including an igniting resistor and a fuse head applied thereon. At first, the electric energy is stored in the capacitor and at a predetermined timing after the electric blaster has been stopped, the switching element is made conductive and the electric energy stored in the capacitor is discharged through the igniting resistor to ignite the detonator.
In the known electric detonator of delay type, it is very important that the amount of electric energy stored in the capacitor, i.e. the terminal voltage across the capacitor, is in a normal operation range. That is to say, when the terminal voltage across the capacitor is lower than the lowest voltage of said normal operation range, even if the blaster is actuated, a sufficiently large current does not flow through the igniting resistor and the detonator is not exploded. To the contrary, when the terminal voltage across the capacitor exceeds the highest voltage of the normal operation range, the electronic delay circuit might not work satisfactorily. Particularly, when the leg wires are erroneously connected to the domestic power supply line, i.e. to A.C. 100 V socket, the electronic delay circuit might be broken, and in the worst case, the detonator might be exploded accidentally.
Heretofore, the safeguard is effected only given the caution or warning that the detonator should never be connected to supply sources other than the specified one. However, this measure is not sufficient for providing the protection against the mis-operation.